**3.2 Autonomous underwater vehicle**

*Earth Crust*

**3. Deep sea vehicles**

survey, target search, and other fields.

phology of the seafloor.

**3.1 Deep tow**

At present, commercial BSSS for deep-sea underwater vehicles mainly includes IOACAS HRBSSS, Teledyne Benthos C3D, and Kongsberg GeoSwath Plus. The highresolution BSSS developed by IOACAS can simultaneously obtain high-resolution seafloor topography and geomorphology, and is suitable for use in complex conditions in the deep sea. HRBSSS has been successfully applied to various deep-sea underwater vehicles such as Jiaolong HOV, DTA-6000 acoustic DT, and Qianlong I/II AUV. A comparison of typical BSSSs for deep sea underwater vehicles is shown in **Table 3**.

Four types of vehicles, on which seafloor mapping sonars can be mounted of deep sea surveys are the deep tow, the automated underwater vehicle (AUV), the remotely operated vehicle (ROV), and the human occupied vehicle (HOV).

A deep tow (DT) system is a large-scale marine equipment used for surveying

the characteristics of the seafloor in the deep sea. It is generally placed nearseafloor using a towing cable to investigate high-precision topography, superficial geological structures, flow fields, and other physical and chemical parameters. A DT system consists mainly of a deck control unit, a winch, cables, a depressor, and a tow body, as shown in **Figure 4**. The A-shaped frame on the mothership is used to drop the tow body into the sea. The towing speed is less than 5 kn. In general, the distance between the tow body and the seafloor is controlled to approximately 50 m, and the mothership moves to pull the DT for topographical and hydrological data collection. The collected data are transmitted to the deck control unit of the shipboard laboratory for processing using a winch and armored photoelectric composite cable. The mothership supplies power to the tow body using the armored photoelectric composite cable. Therefore, the DT system can be used for long-term continuous operation and is widely used in deep-sea

The tow body can be used as a carrier to carry topographical or hydrological survey equipment as needed. Micro-topographical mapping sonars (such as MBE, SSS, BSSS, and sub-bottom profiler) installed on the DT can detect seafloor topography near the seafloor and obtain more accurate topography and geomor-

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**Figure 4.** *Deep tow system*

AUVs (**Figure 5**) are autonomous underwater vehicle that can move in the ocean without real-time control by human being. The AUV itself carries energy and detection equipment and can achieve autonomous navigation and detection operations, less manual intervention, and low mother ship requirements. It is very suitable for largearea underwater exploration and data acquisition operations. The AUV is equipped with relevant sensors for different detection purposes, including acoustic, chemical, hydrological, and geophysical sensors. With the maturity of AUV technology, the AUV is currently equipped with micro-topographical mapping sonars, such as MBE, SSS, and BSSS to near-seafloor to measure underwater terrain as a new option.
